Robust Evidence of Insect Declines

but it had limitations: the sampling of sites was opportunistic and not always consistent over Conservation time, and although the biomass of the speci- mens caught was recorded, the species were Robust evidence of not identified or even counted, meaning that species richness and abundance couldn’t be assessed. insect declines Seibold and colleagues finally complete the circle by reporting species richness, abundance and biomass for a wide range of arthropod taxa William E. Kunin recorded using standardized sampling1. They Data are mounting that document widespread insect losses. describe the results of monitoring over nearly A long-term research project now provides the strongest ten years of intensive study in grasslands and evidence of this so far, and demonstrates the value of woodlands in three regions of Germany as part of the country’s interdisciplinary Biodiversity standardized monitoring programmes. See p.671 Exploratories project10. The results show clear evidence of substantial declines in arthropod abundance There are certain times in life — whether in our Analytical techniques can use such records to and biodiversity (Fig. 2). Grasslands were relationships, personal health or scientific assess changes in the local species richness3 or particularly badly affected: species richness research — when we think that we know some- species’ distributions7, but analyses of this sort of arthropods fell by 34% over the monitor- thing but the evidence is less than conclusive. are frustratingly indirect. The models used to ing period, and the arthropod biomass and An accumulation of clues or symptoms might analyse data can attempt to take into account numbers recorded dropped by 67% and 78%, suggest a particular interpretation without the often strong temporal and spatial biases respectively. These declines were particularly being strong enough to clinch the argument. In in these data sets. However, such results could strong in landscapes dominated by farmland, such situations, it can be a relief to finally get a still be influenced by changes in the nature of suggesting that agricultural management definitive answer, even if the news is bad. Once the biodiversity recording over time, fuelled by could be driving this drop. The losses among we know that a problem definitely exists, we changes in observers’ goals and methods. Such forest-dwelling arthropods were less pre- may be able to do something about it. Read- analyses are also limited in scope. Although cipitous by comparison, with a 36% drop in ers might feel the same way when they read they can reveal changes in diversity, such data, species richness, a 41% loss of biomass and no the results reported on page 671 by Seibold recording a glimpse of a species at a given site statistically significant population decline. et al.1, which provide compelling evidence of on a particular date, do not reveal shifts in The verdict is clear. In Germany at least, insect a major problem — large-scale declines in the insect abundance, which is arguably the most declines are real, and they’re every bit as severe numbers and diversity of insects and other crucial aspect to assess when monitoring as had been feared. jointed invertebrates known as arthropods. ecosystem services8. Such long-term standardized monitoring Insects have pivotal roles in terrestrial Standardized sampling can fill that gap. A as carried out by Seibold and colleagues is not ecosystems. These organisms dominate global previous study9 reported the data collected cheap. However, the expense is dwarfed by the animal biodiversity in terms of their biomass, from a network of standardized insect traps expenditure needed to address the problem. species numbers and total population num- set by amateur entomologists in German Agri-environmental programmes in the Euro- bers, and they perform important ecosystem nature reserves over a 27-year period. That pean Union, for example, spend tens of billions functions and services such as pollinating flow- study indicated that the biomass of insects of euros to encourage farmland biodiversity, ers, disposing of dead organisms and waste, captured declined by 75% over the period a substantial portion of which is aimed spe- and forming crucial links in food webs. Insect studied. This research raised serious concerns, cifically or partially at insects (see go.nature. declines have been implicated as possible drivers of declines in insect-eating birds2 and in animal-pollinated plants3. Thus, massive losses in insect diversity (Fig. 1) and abundance would be grounds for serious concern. The rumours of such declines have been around for some time. In the 1990s, researchers warned that extinctions among insects probably outstripped those of more highly studied organisms such as vertebrates and plants4. Evidence subsequently grew of declines in particular insect groups, including butterflies5 and bees3. Most such studies have focused narrowly on particular insect orders or families, although a recent global meta-analysis6 provides strong indications that insect losses are geographically widespread and occur across a range of taxonomic groups. However, much of this evidence has come

ROD WILLIAMS/NPL ROD from biodiversity databases — records of species sightings, mostly collected by volunteers, Figure 1 | The meadow plant bug, Leptopterna dolabrata. Rumours of a decline in the numbers of insects and usually gathered in a haphazard fashion. such as the meadow plant bug are a cause for concern.

News & views monitoring were rolled out more widely across Arthropod Decline in Decline in Decline in number Europe and beyond, we could begin to build habitat species richness biomass of individuals land-use and agricultural policies on the basis Grassland 34% 67% 78% of compelling scientific evidence. The results reported by Seibold and colleagues might not Forest 36% 41% 17% be good news, but at least now we know where This decline is not we stand and what we should start to do. statistically significant William E. Kunin is in the School of Biology, Figure 2 | Arthropod declines recorded in Germany. Seibold et al.1 report nearly a decade’s worth of University of Leeds, Leeds LS2 9JT, UK. standardized sampling of arthropods — jointed invertebrates such as insects — at grassland and forest sites. e-mail: [email protected] The authors provide compelling evidence of declines in arthropod populations over time. These large-scale changes will probably have a negative effect on key ecosystem services such as pollination. Seibold and colleagues found that species richness and biomass declined significantly during the course of the study in both types of habitat, as did the number of arthropod individuals recorded at grassland sites. The decline in arthropod population sizes noted at forest sites was not statistically significant. com/35pvdtv). Similarly, EU restrictions on the actions and to adjust them if necessary. 1. Seibold, S. et al. Nature 574, 671–674 (2019). 2. Hallmann, C. A., Foppen, R. P. B., van Turnhout, C. A. M., use of neonicotinoid insecticides were insti- The Biodiversity Exploratories project de Kroon, H. & Jongejans, E. Nature 511, 341–343 (2014). tuted specifically to protect insect pollinators, would be a good model for such an effort. 3. Biesmeijer J. C. et al. Science 313, 351–354 (2006). and (industry-funded) research11 suggests that This is because it extends beyond popula- 4. Thomas, J. A., Morris, M. G. & Hambler, C. Phil. Trans. R. Soc. B 344, 47–54 (1994). this restriction has cost EU oilseed-rape farm- tion monitoring to provide a platform for 5. Maes, D. & Van Dyck, H. Biol. Conserv. 99, 263–276 (2001). ers more than €500 million (US$549 million) cross-disciplinary science to address the 6. Sánchez-Bayo, F. & Wyckhuys, K. A. G. Biol. Conserv. 232, annually, because of reduced production and large-scale and long-term issues that are 8–27 (2019). 7. Isaac, N. J. B., van Strien, A. J., August, T. A., the consequential increased costs. crucial in driving declines of insect commu- de Zeeuw, M. P. & Roy, D. B. Methods Ecol. Evol. 5, Ignorance is expensive. Given that substan- nities, but which aren’t amenable to analysis 1052–1060 (2014). 8. Winfree, R., Fox, J. W., Williams, N. M., Reilly, J. R. & tial investments of public and private funds for by controlled experimentation. The project Cariveau, D. P. Ecol. Lett. 18, 626–635 (2015). insect conservation are deemed appropriate not only helps to document declines in insect 9. Hallmann, C. A. et al. PLoS ONE 12, e0185809 (2017). by society, then surely it is sensible to spend a populations and biodiversity, but also assists 10. Fischer, M. et al. Basic Appl. Ecol. 11, 473–485 (2010). 11. Noleppa, S. et al. Banning neonicotinoids in the European tiny proportion of such funds on monitoring, with diagnosing their potential causes. If such Union. Research paper 01/2017 (HFFA Research GmbH, allowing us to assess the effectiveness of these in-depth, landscape-scale field research and 2017).

nature podcast

The week’s best science, from the world’s leading science journal.

NATURE.COM NATURE PODCAST

A80540